January – Emmanuel Joseph Sieyès publishes the pamphlet What Is the Third Estate? (Qu'est-ce que le tiers-état?), influential on the French Revolution.
January 7 – The 1788-89 United States presidential election and House of Representatives elections are held.
January 9 – Treaty of Fort Harmar: The terms of the Treaty of Fort Stanwix (1784) and the Treaty of Fort McIntosh, between the United States Government and certain native American tribes, are reaffirmed, with some minor changes.
January 21 – The first American novel, The Power of Sympathy or the Triumph of Nature Founded in Truth, is printed in Boston, Massachusetts. The anonymous author is William Hill Brown.
January 23 – Georgetown University is founded in Georgetown, Maryland (today part of Washington, D.C.), as the first Roman Catholic college in the United States.
January 29 – In Vietnam, Emperor Quang Trung crushes the Chinese Qing forces in Ngọc Hồi-Đống Đa. It is considered one of the greatest victories in Vietnamese military history.
February – King Gustav III of Sweden enforces the Union and Security Act, delivering the coup de grace to Sweden's 70-year-old parliamentarian system, in favor of absolute monarchy.
February 4 – George Washington is unanimously elected the first President of the United States, by the United States Electoral College.
March
The first version of a graphic description of a slave ship (the Brookes) is issued on behalf of the English Society for Effecting the Abolition of the Slave Trade.
In Southern Africa, the Second Xhosa War between the Xhosa people and European settlers begins.
March 4 – At Federal Hall in New York City, the 1st United States Congress meets, and declares the new United States Constitution to be in effect. The bicameral United States Congress replaces the unicameral Congress of the Confederation, as the legislature of the federal government of the United States.
March 10 – In Japan, the Menashi–Kunashir rebellion begins between the Ainu people and Japanese.